Speed control mechanism



Nov. 20, 1956 w. H. CLARK, JR Y 2,771,286

SPEED CONTROL MECHANISM Filed Jan 19,v 1955 3 Sheets-Sheet l JOI/REE OVER/vak P P :A @25259 i .30 gard 5C. Z

t, D5 /35- AS/y Il /Zd 20;- D/ /0/ PP SC 58 .S C G M I lg E p2 INVENTR WILL/AM H CLA/FV( J1? ATTORNEY Nov. 20, 1956 Filed Jan. 19, 1953 W. H. CLARK, JR

SPEED CONTROL MECHANISM 3 Sheets-Sheet 2 INVENTOR.

ATTORN EY Nov. 20, 1956 w. H. CLARK, JR 2,771,286

SPEED CONTROL MECHANISM Files Jan. 19, 195s 3 sheets-sheet s INVENTOR.

/'/ 7 75 .-j ATTORNEY United Sttes Patent() SPEED coN'rRoL ivmcHANisM William H. Clark, Jr., Rutherford, N. J., assignor to Curtiss-Wright Corporation, a corporation of Delaware Application January 19, 1953, Serial No. 331,990

7 Claims. (Cl. 264-5) This invention relates to acceleration stabilized anticipatory speed control or governing mechanisms of general application, and also to such mechanisms as are particularly suitable for the controlof gas turbine-propeller power plant combinations as used in aircraft.

The invention comprises improvements over those disclosed in Robbins Patent #2,667,344, granted January 26, 1954 and over Mergen, et al. Patent #2,720,927 granted October 8, 1955. The Robbins patent shows a mechanical system for comparing the speeds of a prime mover and of a reference speed device from which is secured a speed error signal. The patent further provides mechanical devices for ascertaining the rate of change of speed error, and for adding, algebraically, the speed error and the rate of change of speed error, productive of a speed correcting signal utilized for controlling the speed of the prime mover. includes speed error and acceleration stabilization. The Mergen et al. patent shows a somewhat similar arrangement to which has been added an alternative means for securing reference speed. One or the other sources of reference speed may be utilized, one of these devices being considered as a standby speed reference useable upon failure of the primary speed reference.

In both of the foregoing systems, the stabilizing signal is secured from the speed reference and for an installation which is intended at all times to run at the same constant speed, both systems afford excellent control. Where the power plant is expected to operate at different speeds, the speed reference must be variable during operation. In this case, it is necessary to insert delay mechanisms to prevent overspeeding or underspeeding, to delay the response of the system when adjustments are made in the power level of either one of the reference speed devices. In other words, the speed setting delay mechanism is necessary in the above mentioned control arrangements to cause the speed setting to lag the power .v

plant speed during a power change wherein there is a simultaneous change in the speed level at which the power plant is to operate and in the level of power to be delivered by the power plant, usually secured by a change in the amount of fuel liow to the power plant.

lf the change of speed setting were not delayed during 4a call for increase in speed and power, the system calls for (l) an initial reduction in power plant load due to the speed error when the power plant speed is less than the called for speed, and (2) a decrease in power plantl load as a result of the acceleration stabilization. The decrease in power plant load at this time is not wanted;

` rather, an increase in power plant load is needed to absorb the increase in power available and to prevent overspeeding of the power plant.

The above indicated delay in speed change slows down the response of the system when speed and load changes on the power plant are demanded.

If the signal for acceleration stabilization is made independent of speed change demands from the governor The speed control thus.

"ice

system, the above mentioned difficulty may be overcome. This may be accomplished by providing a speed reference which is constant at all'times, and which is independent of the power plant speed control, and which is used to derive an acceleration stabilizing signal. This latter signal may then be combined with the speed error signal, the final signal being used to control power plant speed. With such an arrangement, the acceleration stabilizing part of the system ignores a call for a changed level of power plant speed and, upon a change in power plant speed will immediately call for a change in power plant load. For instance, the stabilizing system will call for an increase in power plant load with a call for increase in power plant speed while, at the same time, the speed error part of the system will call for a decrease in power plant load when the call is made for increased power plant speed. The acceleration signal will overcome the speed error signal and will result in increased engine load if the acceleration signal strength is high with respect to the speed error signal strength.

The changes required in the systems shown in the previously mentioned pending applications are not particularly great in order to achieve improved performance in a changeable speed power plant.

Reference may be made to the drawings for a better I understanding of the character of the invention. ln the drawings, similar reference characters indicate similar parts and:

Fig. l is a diagram of the general case for accomplishing the objects of the invention;

Fig. 2 is a diagram of the invention wherein the constantspeed source for acceleration stabilization is derived from the variable power plant speed and wherein the reference speed is derived alternatively from an adjustable device or from the governed constant speed;

Fig. 3 is a diagram of the invention wherein both the constant speed for acceleration stabilization and the reference speed are derived from a separate reference speed source;

Fig. 4 is a diagram of the invention wherein the constant speed for acceleration stabilization is derived from the power plant and where reference speed is alternatively derived from the power plant or from a reference device;

Fig. 5 is a diagram of the invention wherein the constant speed is derived from the power plant and wherein the reference speed is also derived from the power plant;

ythe general case for acceleration stabilization of the system using a constant speed source and wherein power plant speed is compared with a reference speed derived from a reference speed source. Herein, a power plant 10 is provided with an auxiliary output shaft 11 which drives a speed changer 12. The speed changer, which may be of any suitable type, has an output shaft 13 driving a gear 14 of a differential D1. As shown schematically, the speed changer may comprise an input disk 15 and an output disk 16 spaced therefrom, the disks being frictionally engaged by a planet ball 17 whose axis of rotation 18 may be shifted by a tilting control element 19. This is the same type of speed changer as is shown in Mergen et al. patent above mentioned.

Another side gear 20 of differential D1 is driven-in opposite direction to gear 14 from any appropriate de- `from the power plant.

.differential. .carries pinions meshing with the facing gears such as 14 and20 .of D1.

3 vice 21 which operates at a xed constant speed. The output spider 22 of differential D1 will rotate at a speed representing the difference between the speed of the shaft 413 -.and the constant speed. The outputi22-of the .dif-

ferential Dlis drivably connectedto the. ratio changer. 19

of the speed changer l2 ina manner-so thatthe speed :changer ratio is shiftedto stop movementof the output :22 of the differential D1. For any-power plant Vspeed Vthere is a corresponding-ratio of such `speed to the con- `stant speed,.and hence, there is a particular setting for. the

.speedchanger 12 to stop movement of the differential output 22. Thus, said output assumes theposition which represents ratio of power plant speed to constant speed -and .alsothe power plant speed itself, since the constant Ispeed does not vary. The-speed and movement'of output.22, then, represents the rate of change oflpower plant `speed and Aconstitutes an acceleration signal which is carvried to an input gear of a diierential D3.

.The power vplant 10 is also drivably connected to an yinput gear of a differentialDZ, the other input gear of which isdriven vin-opposite direction by an adjustable .referencespeed device .24 .whose speed-.may beregulated by a control 25. .The devi-m24. is .chosensothat it will .operate at a selectedconstantspeed-within a. desired speed range, the speed selection being made to control the desired speed. ofthe. power plant. T he. output ofdiiferential D2, which represents ,the speed error betweenthe Vpower .plant 10 and thereference speed source 24, lis drivably connected to the other input gear of differential D3. The differential D3 algebraically sums the acceleration signal vfrom differential Dl and the speed error signal from vdif- .ferential..D2 so that he output of differential D3 .attains a position which calls forthe speed correction required. The output of differentialD3 is connected at 26 to a speed regulator Y27.01: the power plant lil.

lWhen this system is applied to .an aircraft power plant driving a controllable .pitch propeller, speed control of the power plant isaiorded by alteration of propeller pitch. This is the same thing as alteration of the driven load on the power plant and its purpose is to adjust the driven load so .that it will absorb the power available The position of the .element 26, the output of the differential D3, calls for .the specie blade angle which is required tohold the power plant speed atthe level calledfor by the adjustable reference speed, and at the power for which the power plant is set to operate. The ratios of driving connectionsin the control are selected to provide optimum performance.

The diferentials"D1,`D2 and'D3in`Fig. l and also n other ligures of the drawing have been conventionlized for simpliication in the showing. 'In each showing of the diterential, the member corresponding to 22 injDl is.` the output member and is represented by a'bar across the This member is usually thespider which The driving connections between the Velementsin the figures .are shown in single solid lines, the direction of Vpower `transmission being indicated .by arrows. The

actual driving connections in a working embodiment of :the invention may be of any preferred type, lsuch as shafting, gearing, or other mechanical, hydraulic, electrical,

or `combined transmission means.

In Figs. 2-7, speed changers are identified as blocks containing the ini-tials"SC. All such speed changers may be of the form schematically shown inFig. 1 or may beof alternative design as knownin the art.

In allof the iigures, the dilerentials'D1,D2,.and D3, and the speedchanger 12, have the same relationship and serve the same joint function.

'Tovisualize the functioningof the invention, vthe ensuing vexplanations may be followed. `In a `r`st case, let

it be assumed .thatthe constant speed source 21.and the adjustable lspeed source 24 are in operation at dierent speeds Yand that Vthe power plant is operating at a-set y power level and at a speed which is the same as the speed of the source 24. This, of course, represents an onspeed condition wherein ,no speed correction is being made. The output of the diierential D1 will be zero and the speed changer 12 will be adjusted to a ratio such that the speed changer output in R. P. M. is the same, but in opposite direction, tothe .output of the constant speed source 21. ,Since powerY plant speed and reference speed are the samefand in opposite' direction,A the output of the diierentialDZ isizero.

- Now, .should there be: a transient-.disturbance infpower plant vspeed whereby its R. P. M., let us say, increases, a speed error will be sensed by diierential D2 vand acorrective signal will bepassedto the .dilerential D3, calling for increased driven load on the power plant. For this example we will assume that the power plant drives a controllable pitch propeller and consequently, the differential ...D3 `willcall for 4.anincreased .propeller blade angle to 4bring the R. P. M.back=to normal. '.Concurrently the .dif-

.ferential .D1-will register the initial acceleration ofthe .power planttoward,theyinereased speedto; cause movement of the output of dilerential 13.1,: simultaneously shifting-the speedfchanger to-.bring the `diiferentialoutput` to .zerand vpassing the a'ccelerationfsignal 1 to. differential D3. This .signal will initially be a positive acceleration signal during .the transient increase-in power plant. speed and will calLfor increasedpropellerpitch. .':As speed is corrected and the power l,plant decelerates, .the `sign of the acceleration .correction'willchange'to negative, the deceleration signal being-minus with respeetto thespeed ,error signaland otisettingratleast in'zpart-the. speed error signal which is plus. As .the-speederror decreases due'toapproach of .thel power plant torthe .on-speed condition the accelerat-ionandspeed errorsignals will equalize and bladepitch correction will cease and probably reverse directionrbefore .the powerrplant reaches on-speed. The blade angleset- Vting due to this action will,r probably overshoot that which is required tomaintain the reference R. P. M. butwill `quicklyreturntothe required pitch. Thereby the excess -load `torque during the pitch overshoot-decelerateszthe power plant rapidly toward the referencespeed. The reverse ofrpitch change before'the powerplant reaches on- ;speed allowsrthe blade .angleto return tothe inal setting at substantially the same time as. the power plant reaches on-speed. Thisaction: prevents hunting as the final lSpeed is reached. The acceleration Vsignal-providesanticipatorfy V.control to expedite theattainmentof on-speed without humilla Iffthe transientspeed error is inthe oppositedirection, thatfis, a decrease in speed, the same action as v.above `described willoccur except/in reverse directions.

.If the power plantis operating at a steady state .con-

.dition andanincreaseis .made inthe referencespeedby .adjustment f of the. speed source 12.4, without anyy concurrentfchang'ezinthe fuelsetting of thepower plant, anun- .derspeederror will .be registered bythe differential D2 which is .transmitted to the differential .D3 tocause .a

.correction ..in..power plant speed .by decreasing load or bladeangle. The. acceleration signal from differential D1 does notappear until .an .actual change in powerplant speed ,is .accomplished [whereupon .the positive .acceleration andfminus .speed -error signals .are summed in the dif- .ferential D3 .to correct the blade pitchsettingin the and the steady state condition will be attained as described previously. Then, pitch change will cease and thepower plant will reach on-speed without further pitch change or load correction.

If the power plant is operating at a steady-state condition and a decrease in reference speed is made by adjustment of the speed source 24, with no concurrent change in fuel setting of the power plant, the blade pitch angle will be increased by the speed error in differential D2 and negative acceleration will anticipate the speed correction through its transmission from the differential D1 to thc differential D3.

If the adjustable reference speed is changed concurrently with a change in power setting for the power plant, let us say in a power and speed increasing direction, the differential D2 will register an underspeed error calling for decreased blade pitch to enable the power` plant to be accomplished by vincreasing blade angle in the manner previously described. When the delay device is inserted in the Mergen et al. system,y the increase in power and called for speed creates positive acceleration and a call for va positive speed error so that blade pitch is increased immediately; However, the insertion of the delay device while making the system fully satisfactory from an operative standpoint, injects added complications and variables.

Thus, it will be appreciated that a principal object of the present invention is to provide a simple derivative speed control system which depends upon operating conditions and eliminates arbitrary delay factors which are necessary in the device of the prior art.

For clarification of the foregoing explanation, a tabulation follows which shows the direction of change of blade angle, called beta for various operating changes.

Sign of Etect of Control conditions of power plant; speed speed error Sign of Effect of acceleration on Net effect on blade angle error on blade acceleration blade angle angle Transient underspeed xed power Less 1 lstsicgges ';;t'gigg ogjjj }Less Transient overspeed xed power Greater rrlifgges'egggt'ih'g55:: }Greater Increased speed setting fixed power setting Less Anticipates new setting of Less Decreased speed setting fixed power settm Greater... ..-1.510 Greater l Increased speed and power setting Less Inmates greater Starts correctioni to tpigri/ ent overspee an s a 1 izes l l at required new Decreased speed and power setting Greater.. Imtlates less Start correcion o 1:prbeirlent v un erspee an s a izes In Cat required new B. Increased power setting fixed speed setting..... Increeses. AlffcaijtggH,'iHXf-"I gfofrflew to ab' Decreased power setting txed speed setting..- Decreases. l lirel'l';gf: Do.

gain speed. However, since power is being increased along with speed, it is necessary to increase rather than decrease blade pitch so that the propeller may absorb the additional power available from the power plant. As the power plant responds to the increase in fuel feed it will accelerate thus producing a positive acceleration signal in the differential D1 which is transmitted to the differential D3 in a direction to call for increase blade pitch.

The gearing of the several dilferentials is so arranged that this signal will be stronger than and will overcome the negative speed error signal from the differential D2 so that increased blade pitch will actually be called for in the controllable pitch propeller to absorb the increased power.

Since the desired speed lever has also been raised, the signals from the differentials D1 and D2 will combine in the differential D3 to call for the blade angle for the power plant which will produce stable power plant operation at the new speed and power setting.

If power and speed are concurrently decreased, the opposite effects from those above described will be secured so that propeller blade angle will end up at the proper value to maintain the new speed setting for the power being developed by the power plant.

lf the constant speed source 21 were replaced by the .adjustable reference speed, as in the disclosure in Mergen -et al. patent it becomes necessary to insert a delay device such as a dashpot between the speed reference and the differentials toavoid a tendency toward overspeeding in the case of a change in power and speed.

If this delay device were not use, a call for increased speed and power would result in a negative speed error calling for decreased blade angle and would also call for a decreased blade angle due to negative acceleration at the start of the cycle. This would permit overspeeding even though the last part of this cycle, after the power plant begins to accelerate, would call for an increase in blade angle due to the positive acceleration. The power -plant would overspeed and speedcorrection would then There are Various means by which these results may be accomplished practically, which are shown in Figs. 2-6. Fig. 2 shows in effect, a modication of the system of said Mergen et al. application. In Fig. 2, a governor 28 is driven by the power plant and strokes the ratio changer of a speed changer 30 which is also driven by the power plant. The governor has a non-adjustable Speeder spring 29 so that the output 32 of the speed changer 30 is always maintained at a constant speed. This output 32 provides the input to the right side of the differential D1 so that the system then operates in the same fashion as the system shown in Fig. 1. In this case, the adjustable speed reference `source 24 is connected to the differential D2 through a clutch 34 and when so connected this system operates as does the system of Fig. l. In case of failure or disconnection of the reference speed source (ARS) 24 from the system, the drive to differential D2 may be arranged to disconnect automatically from the reference speed source, and to connect to the constant speed output 32 of the speed changer 30 through a clutch 35, as in said Mergen application. This enables standby operation of the system at the constant speed for which the governor 28 is set. A limitation in this type of standby system is that when it i-s operating under emergency conditions there is no speed flexibility for the power plant. Under certain circumstances, this is not a significant limitation. The clutch 34 becomes unnecessary if the reference speed source is a motor which rotates freely when electrically disconnected from its power supply.

The system of Fig. 2 may be applied with very little change to the system disclosed in the Mergen et al. patent without the addition of any speed changer or differential units and enables the elimination of the speed changer delay device heretofore mentioned along with more rapid response of the power plant to speed and power changes than can be attained with the system disclosed in the Mergen et al. patent.

Another alternative arrangement is shown in Fig. 3

adjustable reference speed source-24. 'in`Fig. l; the adjustable reference speed source is directly connected to the diiterential D2. The device 24 also -drives a governor 36 having a'xed speed setting, this governor serving to control a speed changer 38 which is driven by theadjustable reference speed'source 24.

'speed inputto the right side ofdiferentiai D1.

lgovernor controlling the speed changer.

-wherein the constant speed for acceleration stabilization asl delivered Vto the 'diterenial 'DI isfderivedfromwthe lnlthis casetas The output of the speed changer 3S will run at constant speed as controlled by governor 36' to provide a constant This system would besatisfactory if a'completely vdependable 'and continuously operating reference speed source 24 is available.

In the arrangement'of Fig. 4 the power plant drives a Xed-setting governor 28 and'a Speed changer 30, the The output of the speed changer 30 operates at constant speed and drives the right hand input gear of the differential D1 to provide the desired operating characteristics for the accelera- 'tion responsive part of the system, vas in Fig. 2. The adjustable reference speed source 24 may normally be conynected to drive thedifferential D2 through a clutch 34.

An additional speed changer 42 is provided, driven at constant speed by the speed changer 30. .The speed changer 42 is selectively adjusted to a ratio sothat its output provides a reference speed of desired value connectable at times or as desired to the differential D2 through the driving connection 44 and clutch 46. The clutches 46 and 34 operate reciprocally and preferably in response to failure or stoppage of the device 24, so

"that it the latter, which is normally connected to the diierential D2, fails, the system is immediately connected to the speed changer 42. Preferably, the speed control for the device 24 and for the speed changer 42 are-interconnected by a suitable linkage 48 so that the speed changer 42 and the device v24 will both'normally `call for the same reference speed.

The reference speed source 24 maybe part of synchronizing gear for a plurality of powerplants whereby :thereferencespeed from speed changer 42;may be used for standby purposes. Alternatively, for a single power plant system, the changer 42'may drive diierential D2 directly, omitting the elements 24, 46 and 34.

Fig. shows a variation in the system wherein a fixed setting governor 28 is driven by the power plant 10.and controls the speed changer 30 also driven bythe power plant 10. The speed changer 30 drives the right vside of differential Dias previously and the lett side of D1 is -driven through a speed changer 12 from the power plant. 'This provides the same acceleration responsive control las previously described. The right side of differential vD2 is also driven fromthe speed changer 30 througha driving connection 50 sothat the rightend .of the ydiffer- -ential D2 rotates .at a xed constantspeed. The 'power plant also drives a speed changer52 through a driving con- .nection 54, the output from thespeed changer 52 driving Ythe left end of differential D2 through a` driving connection 56. The differentials D2 and D1 are connected into ythe diierential D3, and the output of differential D3 controls power plant driven load as previously described.

The speed changer 52 is manually controllable by an .adjuster S8 yso that its ratio may selectively be made greater or-less than l. The adjusteriS thus establishes .-a relationship between power plant speed anda xedconstant speed established by the speed changer 30. For instance, ifxthe iixed constant speed is l0,000R. P. M., a ratio of 1:1 in the speed changer 52 would :require the power plant to operate at 10,000 R. P. M. and any Vdeviations from this speed would actuate the control system to-correct power plant driven load to yrestore the `10,000 R.v P. M. .operating speed. lf .it weredesiredto operate the powerV plant at 11,000.12.. .P. M. ythe speed changer would be set at a ratio of 1.1:1.0. .Any deviation :fronti the arbitrary 210,0.00=.R. -inatherlrivingt-connecftion-"56'1would register a4k speed errorltandx would 'correct -`powerfplant speed? tofa level such'thatthe' driving'fcon- 4nection 56 is at lOLOGO-RsfRVM. #Thisnecessai-ily means that the power plant would have to operatef-at'fllgUOO R. P. M. vto'.yiel:l 10,000 RJPLf-M; in the'driv-ingf'connection 56. In the samelfashion, ifthe'speed-'changer were set to a ratio of 0.9:1`L0 thepower plant-would-befon speedlat 9-,000R. P. M. .and wouldv thereby produce'l0,000

`R. P. M. inl the driving connection 56 to match the fto speed ernor and acceleration-errorisl the 'sameasy that previously described.

Figs. 6 and 6a show -a controlsystem'ampliedfromthe disclosure of Fig. 5 wherein the system is adapted for synchronization with one or more additional power plants, utilizing a master refe-rence speed sou-ree in the orm of a polyphase generator 6G. The differential assemblies D, D2, and D3 have been omitted in Fig. 6 but are connected Vto thepower plant andY to Ithe speed changers 30, 12 and 52, in the same manner as shownin Fig. 5.

The generator 60 drives a synchronous motor62 at synchronous -speed therewith, the motor 62 driving "the left 4handiinput of' a differential D4. lThe power'plant drives the right hand input ofthe differential'D4. .-Any speed error between the power plant and the synchronous motor is reilectediinrotation 'of-the output=e1ernentf64 of differential D4.

The output element 64 drives :a slip clutch 66 which imposes speed error 'on an input element 68 of a dif- `'ferential D5. 4Theinput elementis limited to' a's'mall rangerof rotation by a lstop arrangement 67. -Theother input element of differential D5 is normally fixed so that any motionin-.the'input element 68 is transmitted to the output element 72 of the differential D5. -Thisfin turn is drivablyconnected to the -.speed changer 52-s0 `thatthe outputfelement 72 adjusts the speed changer-+52 in response tospeed errors between the power plant 'and the synchronous motor, to a value to-produce a certain .speed in the output of S2 fromthe ispeed of the-power plant. If this certain speed varies fromthe `-outputfspeed -of-speed ychanger 30, power plant speed correctionv will result until power plant speed is the sameassynchronize-r speed. This condition, .through differential` D4, 'holds f the ratio 'of speed changer 52 at the proper value.

From here on, thesystern operates in the same-.manner as that described in connection with Figure 5. InFig. 6a, substantially .the same system is shown `and thesame reference characters are used predominantly. The `right handfpowerplant and its controls use unprimedreference .characters while the ysimilar elements'in the Ileft hand power plant use prime referencefeharacters. In Fig. 6a, a motor 59 is shown as driving the generator 60,-1 the 'motor being of'adjustable speed type.

The generator'60 may be .used as the .masterfspeed reference for a; plurality of power plants, the generator being connected to other synchronous-motors like motor 62, through leads 74.

tion` ofthe input to the rdiierential D5. Thereupon;ad :justment for the .speed `level of. thet power plant may-be ,-alorded by antanual lever'76 which-adjustshefdifferential input 70iand consequently the ratioloffthe speed changerrSZ. The control 76 isJequivalent.toltheFcontrol 'fnot .operating 9 either the'control lever 76 or 78 to establish the synchronous desired speed for both power plants.

Ordinarily, the controls for a plurality of aircraft power plants driving propellers are so connected that each power plant has its own individual power control, the power control coordinating on a xed schedule, the desired power plant R. P. M. land the fuel input to the power plant. When plural power plants are used an interlock arrangement is provided between the -several individual controls so that all power plants will be set to the speed of that power plant whose control lever is farthest advanced. The less advanced controls of other power plants will call for a. lesser degree of fuel feed but all wil-l be set to the R. P. M. level of the most advanced control. This obtains when the power plants are synchronized through the use of a generator such as 60. Other power plants, while operating at the most advanced speed, can be controlled as to power by setting their power levers to a low power position. This yields exibility of operation.

In Figs. 6 and 6a, another power lever 78 for another power plant is shown with an operating link 80 setting the generator 60 to the desired R. P. M. level. In the ca-se of Fig. 6a the link Si) controls the speed of the motor 59 which drives the generator 60. This controls the power plants to synchronize speed. However, in Fig. 6 the control for power plant 10 is set back from the position for synchronous speed as represented by the distance 82. This means that the power plant 10 through the coordinated fuel control will be operating at less power, but at the same speed, as the power plant controlled by the lever 78. When the synchronizer is not in operation, or may have failed, the coordinated speed control, of course, drops out, but each power plant may be individually controlled for power and R. P. M. through actuation of the control levers and through operation of the differentials D5. In Fig. 6a either power lever 76 or 78, whichever is furthest advanced, controls the speed of operation of the motor 59. The functioning of the arrangement in Fig. 6a is the same as that shown in Fig. 6.

IIn the systems of Figs. 5, 6 and 6a, except for operation 'of the synchronizing generator 60, the governed speed of the power plant is derived from the power plant itself through the fixed setting governors 28 without the need for separate speed reference devices.

iIn the arrangement of Figs. 6 and 6a, the differential D4 and the clutch 66 provide `a means for trimming the speed of the power plant to a precise desired level, in

addition to providing a speed and acceleration responsive control of the driven load through `the operation of the diierentials D1, D2 and D3 and associated apparatus.

In the arrangement of Figs. 6 and 6a, the signal strength of the synchronizer part of the system may be low so las not to insert instability into the governing system. The synchronizer may be designed to require several seconds to trim the system to synchronism, whereas the `governor system operates nearly instantaneously. This al-so avoids the causing of drastic power plant speed setting changes due to the synchronizer not operating. Limi-ts may be placed on the rotation of element 68 as at `67 so that mallunction of the synchronizer cannot effect a speed setting diering greatly from the setting represented by .the level 7 8.

In any of the systems described, an yadvantage ows from reducing the load on the adjustable `speed reference, enabling elective use of small size reference speed units.

Further arrangements of the invention, rather obvious in view of the preceding explanations, could be set up as Kfollows:

(l) The elements 42, .24, 48, 46 :and 34 of Fig. 4 cld be disposed in Figs. 5 and 6 or 6a to replace the speed changer 52 and rel-ated mechanisms;

I(2.) The elements '52, 60, 62, D4 and D5 and auxiliaries, in Figs. 6 and 6a, could be used in the arrangement in Fig. 4, replacing the elements 42, 24, 46 and 34.

EFig. 7 shows a trimming synchronizer system which operates in lgenerally similar fashion to that abovede scribed except that either the power plant 10 or 10 may act as the master speed reference, to which rotational speed of the other power plant i-s trimmed. Herein, power plant 10 `drives a generator `84 which may be con- -nected to drive -a synchronous motor 86 through .a switch "88, motor 86 driving the D4 diterential 64'. In similar fashion, the power plant 10 drives the generator 90 which may be connected through the switch 88 to 'drive `the synchronous motor `92 which in turn is connected to the D4 d-ierential 64. The switch 88 is preferably of snap action type, connecting the generator 84 and the motor 86 or alternatively the generator 90 and the motor 92 by actuation of a switch member 94. The latterlis pivotally connected to the middle of a rocker, the ends of the rocker being connected through links 97 .and 98 to manually operable power levers 76 and 78. As shown, Ithe power lever 78' is advanced slightly -ahead of the lever 76', thus throwing the switch 8'8 to connect the generator with the motor 92. This establishes the power plant 10 as the master and the power plant 10 is slaved `to synchronism with the power plant 10 through the trimming synchronize-r mechanism embodying the diierentia-ls D4 and D5 in the control system of the power plant 10. In this situation R. P. M. cont-rol of the power plant 10' is accomplished by the setting of the power lever 78' acting upon the input gear 70' of thel dierential D5. This adjusts the speed changer '52' lto set a desired level `of speed for the power plant 10.

If the power lever 76 is .advanced to the position of Ithe power lever 78', control remains in the power plant 10', but if the power lever 76 is advanced ahead of the lever 78', power plant 10 becomes the master for R. P. M. control and the power plant 10 is slaved thereto. This occurs because `of the shift of the switch 88 which sets up the generator 84 to control the motor 86.

As in .previous embodiments, should the master alten nator or its power plant fail, slave power plants would shift to control by their own governors.

By appropriate mechanisms, the .synchronizing trimming control of Figs. 6, 6a and 7 [can be .expanded to encompass more than two power plant and control systems.

Though several embodiments of the invention are shown, it is to be understood that the invention may be applied in other forms and in various environments. Changes may be made in the arrangements shown without departing from the spirit of the invention. Reference should be had to the appended claims for deiinition of the limits of the invention.

What is claimed is:

1. In a power plant speed control system, a variable ratio transmission driven by and connected to the power plant, a rst dierential having an 4input driven by the transmissi-on output, said differential having a .second input and an output, constant speed means driving 4the second input of said differential, a ratio changer in said transmission driven by said differential output, a second ldiierential hav-ing an input driven by said power plant, an adjustable reference speed source driving -another input of said second differential, a third differential having inputs -driven by the outputs of said lrst and second differentials, and a power plant .spe-ed controller driven lby vthe output of said third d-ilerential.

2. In a power pl-ant speed contro-l system, a constant speed source, an adjustable reference speed source, means connected to the power plant and reference speed source to compare power plant and reference speed productive of a speed error signal, means connected to said power plant and constant speed source to Icompare acceleration of the power plant against the .constant speed source productive of a power plant acceleration signal, means connected to and driven by said two comparing means vfor summing said signals and productive of a combined speed error 'and acceleration signal, and means connected to .threefelementdifferential.having .twoinpnt elements. and

dan outputzelement.

54. ."A system according to.c1aim .2 whereinsaid con- .lstant.ispeed source .comprises-a fxed-setting governor 'driven by thcpower plant .and'a'speed .'chan'gendriven 'lbyzthefpoweriplantf and` including a'ratio change element, fandiacontroldconnection actuatedlby the governor and @connected to 'control .said ratio fchanger.

Ina-.power plant Vspeed 'control-system,.'means to derivei affixed .constantspeedfrom the power plantre- `regardless 4lof `:its rspeed, .means to derive..frorn1said .first :meansa selectivelyv variable 'reference speed, `means k'to .Icomparelthepower plant speedand .thefconstant speed, lm'eans Ito 1 compare .power.- .plant yspeed and the yreference speed,lrisurnrningfmeansz actuated byrsaidla'st two means .iproductiveof ya-Icombinedvspeed correction signal, Yand .meansmctuated by said summingmeansla'nd-by.- said. sigmala-to control; power plant speed.

'6.1In1alpowerplant :speed control system,V a'constant :speed source, aspeed changer drivenbythe power plant,

.comparingfrneansdriven by the speed 'changer and by the means itovcompare :said functionsspeediand:the' speed Lof said power .plant productiveiofa .speed A.er1or.='.outp1t, summing .means connected vtoi said '.two :comparingmeans 1 and .driven thereby..productivey of' afcornbinedrrorzsignal including speed error fand acceleration factors, :fand

`means connectedto said summing means tochangev power plant speedf according to said combined error signal.

7.'. In a' vpov/er plant speed :controlsystem` a constant speedlsource, aspeed changer .driven by the power plant,

`comparing meansdriven by thespeed changer 'fandby .speedsourcefand bysaid powerplantat na functionzof plant speed andhaving a speedserror. output, .and

summing meansconnected. to and drivenby saiditwofoutputs, said summing. means having. an output .operatively connected to change power plant speed.

' References Cited in the-.tile of thisfpatent :UNITED STATES PATENTS 1,520,973 Staegey ..-l Dec.A 30, 1924 2,000,049 "Taylor Q."May 7," 1935 2,248,072 Fry July8f1941 2,494,092 Hayward Jan. 10, 1950 2,595,195 Hosterman Apr. .29, ',119'52 

